It is known for shell-shaped components that have been stiffened by stiffening elements to be partially provided with local thickened portions (referred to below as doublers), in order to absorb high load concentrations in individual portions of the component structure and to distribute these loads throughout the structure. In this context, a distinction is drawn between internal and external doublers.
Internal doublers are applied to the inner side, for example of a component provided with stiffening elements, and therefore have no influence on the outer contour of the component. In this case, the stiffening elements have to run over the doubler, i.e. the doubler and the stiffening components are arranged above one another.
However, in terms of technical implementation, it is only possible to run over a doubler with considerable outlay. Although the stiffening elements can generally be produced with a moderate offset, integration represents a frequent cause of complications during manufacture.
As an alternative to internal doublers on the inner side, it is possible for the doubler to be placed on the outer side of the component. This has the advantage that the complex inner structure of the inner side (reinforcing elements, spar, ribs, etc.) is not adversely affected. However, the outer side no longer has the desired contour, which has an adverse effect on aerodynamics for example in the case of aircraft structures.
Furthermore, the use of external doublers involves a number of manufacturing drawbacks. If the doubler is to be integrated in the manufacturing means, any change to the doubler entails a corresponding adjustment to the manufacturing means.